Drive sprocket, drive lug configuration and track drive arrangement for an endless track vehicle

ABSTRACT

A sprocket for a tracked vehicle. The sprocket has a plurality of sockets for engaging drive lugs on an inner surface of a track driven by the sprocket. The sprocket also including a support surface for engaging with an inner surface of the track and which is in rolling contact with the inner surface of the track.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 USC 119(e) of U.S. Provisional Patent Application No. 61/422,947 filed on Dec. 14, 2010 and U.S. Provisional Patent Application No. 61/426,979 filed on Dec. 23, 2010. These patent applications are hereby incorporated by reference herein.

FIELD OF THE INVENTION

The present invention relates to tracked vehicles in general and more specifically to improvements in drive sprockets, drive lug configurations and track drive arrangements for tracked vehicles.

BACKGROUND

Tracked vehicles, such as heavy agricultural or construction equipment, that routinely operate in rough environments may suffer from rapid track deterioration. As a result of this track deterioration, the track must be replaced or repaired which is expensive and significantly increases the cost of operation of the vehicle over time.

Tracks, especially rubber tracks are subjected in use to different wear patterns that depend largely on the intensity and the type of use of the vehicle. One specific point of failure of the rubber track is the drive lugs. The drive lugs are used to establish a positive drive connection between the track and the drive sprocket. Accordingly, when the track operates at high loading levels, a significant amount of stress is exerted on the drive lugs to impart movement to the track. Over time, this amount of stress can damage the drive lugs ultimately leading to drive lug separation from the track carcass.

SUMMARY OF THE INVENTION

As embodied and broadly described herein the invention provides a sprocket for a tracked vehicle, the sprocket having a plurality of sockets for engaging drive lugs on an inner surface of a track driven by the sprocket, the sprocket also including a support surface for engaging with an inner surface of the track and which is in rolling contact with the inner surface of the track.

As embodied and broadly described herein the invention also provides a sprocket for a tracked vehicle the sprocket having a plurality of sockets for engaging drive lugs on an inner surface of a track driven by the sprocket, the sprocket also including a support surface for engaging with an inner surface of the track and which has a coefficient of friction less than about 0.1.

As embodied and broadly described herein the invention yet provides a sprocket for a tracked vehicle the sprocket having a plurality of sockets for engaging drive lugs on an inner surface of a track driven by the sprocket, the sprocket also including a support surface for engaging with an inner surface of the track and which has a coating of low friction material.

As embodied and broadly described herein the invention also provides a sprocket for a tracked vehicle having a support surface for engaging with an inner surface of the track and an actuator to selectively (1) lock the support surface to the sprocket to engage a friction drive assist mode or (2) unlock the support surface with relation to the sprocket to disengage the friction drive assist mode.

As embodied and broadly described herein the invention provides a sprocket for a tracked vehicle, the sprocket having a plurality of sockets for engaging drive lugs on an inner surface of a track driven by the sprocket, the sprocket including a removable component to laterally open one or more of the sockets such as to allow the track and the drive lugs to be removed from the sprocket by sliding them out along an axis of rotation of the sprocket.

As embodied and broadly described herein the invention provides an endless track having an outer ground engaging surface, an inner surface opposite the outer ground engaging surface and a plurality of drive lugs projecting from the inner surface, one or more of the plurality of drive lugs having opposite lateral extremities and a driving face extending between the lateral extremities for engagement by a sprocket in order to propel the track, the driving face having a projection intermediate the lateral extremities.

As embodied and broadly described herein, the invention further provides in combination:

-   -   a drive sprocket having a generally circular configuration with         a generally cylindrical peripheral surface;     -   a plurality of spaced apart drive pins or bars defining on the         cylindrical peripheral surface recessed sockets;     -   an endless track having an outer ground engaging surface, an         inner surface opposite the outer ground engaging surface and a         plurality of drive lugs projecting from the inner surface for         engagement in respective ones of the sockets, one or more of the         plurality of drive lugs having opposite lateral extremities and         a driving face for engagement by a respective drive pin or bar,         the drive pin or bar having a recessed portion and the driving         face having a projection that engages the recessed portion when         the drive pin or bar engages the driving face.

As embodied and broadly described herein, the invention provides a sprocket arrangement for an endless track, comprising a central hub defining an internal cavity in which are mounted one or more gears for driving the hub. A rim structure is integrally formed with the hub, the rim structure including a plurality of peripherally disposed sockets for receiving drive lugs projecting from an internal surface of the track.

As embodied and broadly described herein, the invention further provides a sprocket arrangement for an endless track, comprising a plurality of peripherally disposed drive pins defining between them sockets for receiving drive lugs projecting form an inner surface of the track, one or more of the drive pins including a core member and a wear jacket to protect the core member from wear as a results of repeated contact with the track.

As embodied and broadly described herein the invention further includes a sprocket arrangement for an endless track, comprising a plurality of components defining a rim portion of the sprocket, the plurality of components being radially moveable to vary a diameter of the sprocket.

As embodied and broadly described herein, the invention further provides a sprocket arrangement for an endless track, comprising a plurality of components defining a plurality of peripheral sockets for receiving drive lugs of the endless track, the plurality of components being selectively moveable to vary a pitch of the sprocket.

As embodied and broadly described herein the invention also provides a sprocket arrangement for an endless track, comprising a plurality of drive pins defining between them a series of peripherally disposed sockets for receiving drive lugs of the endless track, the plurality of drive pins capable of resiliently yielding in when engaged by respective drive lugs.

As embodied and broadly described herein the invention provides a track drive system comprising an endless track; and a sprocket in a driving engagement with the track, the driving engagement including a first positive drive engagement and second positive drive engagement.

In a specific and non limiting example of implementation the first positive drive engagement includes a first set of teeth on the track for engaging corresponding sockets on the sprocket.

In a specific example of implementation the second positive drive engagement includes a second set of teeth on the track for engaging corresponding sockets on the sprocket, wherein the first set of teeth is distinct from the first set of teeth.

In a specific example of implementation the first set of teeth and the second set of teeth have different pitches.

BRIEF DESCRIPTION OF THE DRAWINGS

A detailed description of examples of implementation of the present invention is provided hereinbelow with reference to the following drawings, in which:

FIG. 1 is a side elevational view of an agricultural vehicle using a rubber track;

FIG. 2 is a side view of a sprocket arrangement used for driving a rubber track, showing the relationship between the drive lugs of the track and the sprocket bars;

FIG. 3 is a front elevational view of an alternative sprocket configuration where the cavities for receiving the drive lugs of the track are located in the center of the sprocket;

FIG. 4 is a side elevational view of an alternative endless track arrangement for an agricultural vehicle;

FIG. 5 is a plan view of an alternative drive sprocket configuration.

FIG. 6 is an enlarged fragmentary cross sectional view of the sprocket of FIG. 4 illustrating a possible variant.

FIG. 7 is an enlarged side view of a track illustrating the location of a pressure sensor in a drive lug.

FIG. 8 is block diagram of a computing platform for generating control signals to selectively actuate or de-actuate the friction drive assist mode.

FIG. 9 is a flowchart of a process for managing the friction drive assist mode of the vehicle.

FIG. 10 is a schematical side view of a sprocket configuration according to a variant, and also illustrating in dotted lines the rubber track mounted on the sprocket;

FIG. 11 is an enlarged side view of the sprocket arrangement illustrated in FIG. 10;

FIG. 12 is a schematical side view of the sprocket configuration illustrated in FIG. 10 in which the sprocket has been opened to afford unobstructed entrance and exit to the drive lugs of the track, in order to allow removal of the track and instillation of a new track without the need to dismount the sprocket from the vehicle;

FIG. 13 is a view similar to FIG. 12 but in which one of the side rings of the sprocket still remains on the sprocket;

FIG. 14 is a top fragmentary view of the sprocket showing details of the attachment of a side ring to sprocket spokes;

FIG. 15 is side view of the structure shown in FIG. 14;

FIG. 16 is a top view of the entire sprocket with one of the side rings removed;

FIG. 17 is a fragmentary vertical cross-sectional view of the sprocket illustrating details of the attachment between the side rings and the spokes of the sprocket;

FIG. 17 a is a view similar to FIG. 17 but of a variant;

FIG. 17 b is a perspective view of the variant shown in FIG. 17 a;

FIG. 18 is a fragmentary vertical cross-sectional view of the sprocket illustrating details of the attachment between the side rings and the spokes of the sprocket, according to a variant;

FIG. 19 is a fragmentary vertical cross-sectional view of the sprocket illustrating details of the attachment between the side rings and the spokes of the sprocket, according to yet another variant;

FIG. 20 is a top, enlarged, fragmentary view of a sprocket according to a variant, illustrating the shape of the drive lug receiving sockets and also illustrating in cross-section a drive lug according to a non-limiting example of implementation of the invention;

FIGS. 20 a and 20 b illustrate a sleeve and pin combination;

FIG. 21 is a cross-sectional view of a sprocket according to yet another variant;

FIG. 22 is a cross-sectional view of a prior art sprocket arrangement;

FIG. 23 is an enlarged cross-sectional view of a drive bar of the sprocket according to the invention, which uses a sacrificial wear jacket;

FIG. 24 is a variant of the wear jacket shown in FIG. 23;

FIG. 25 is a cross-sectional view through a sprocket generally of the type shown in FIG. 3, illustrating yet another form of construction using radially adjustable drive pins;

FIG. 26 is an enlarged cross-sectional view of a drive pin of the sprocket shown in FIG. 25;

FIG. 27 is a cross-sectional view of the sprocket according to a variant of FIG. 25;

FIG. 28 is a cross-sectional view of the sprocket according to yet another variant of FIG. 25;

FIG. 29 is a side elevational view of an undercarriage for an agricultural or construction vehicle which uses a rubber track with a dual drive lug pattern;

FIG. 30 is perspective view of a sprocket that drives the track of the undercarriage shown in FIG. 29;

FIG. 31 a fragmentary perspective view of the track of the undercarriage of FIG. 29, illustrating in greater detail the dual drive lug pattern;

FIG. 32 is a cross-sectional view taken along lines 32-32 in FIG. 29;

FIGS. 33 and 34 are plan views of the inner surface of the track illustrating alternative teeth patterns;

FIG. 35 is a cross-sectional view taken along lines 35-35 in FIG. 21.

In the drawings, embodiments of the invention are illustrated by way of example. It is to be expressly understood that the description and drawings are only for purposes of illustration and as an aid to understanding, and are not intended to be a definition of the limits of the invention.

DETAILED DESCRIPTION

FIG. 1 is a side elevational view of an agricultural vehicle which uses a rubber track. The vehicle 10 has an upper body including a cabin for the operator and housing for the power train. The power train can include an engine which can be an internal combustion engine. Alternatively, the engine can include an electric motor. The power train also includes a transmission coupled to the engine. The transmission would typically include a gearbox with clutches allowing controlling the application of drive power to the track.

The vehicle 10 has an undercarriage 12 including a set of wheels about which is tensioned a track 16. The set of wheels has a drive wheel 30 and an idler wheel 32. In a variant, both wheels 30, 32 can be driven. In a yet another variant only the front wheel 32 can be driven. In a further variant described below the undercarriage has several idler wheels.

The track 16 is mounted on the wheels 30, 32 such that as the wheels 30, 32 turn, the track is caused to move. The undercarriage also includes a set of rollers 40 which are mounted between the wheels 30, 32 in order to keep the run of the track 16 between the wheels 30, 32 in contact with the ground. The rollers 40 are mounted on a suspension system 42 allowing the rollers 40 to yield upwardly when the vehicle 10 rides over obstacles.

The undercarriage 12 further includes a tensioning system 44 to tension the track 16. The tensioning system 44 operates hydraulically and includes a hydraulic ram mounted between a fixed portion of the undercarriage and a short arm 46 to which the wheel 32 is pivotally connected. The hydraulic ram includes a casing defining a cylinder bore 47 in which is slidingly mounted a piston 34. As the piston 34 of the hydraulic ram extends, this causes the short arm 46 to move and change the position of the wheel 32 with relation to the wheel 30. If the hydraulic ram is extended, the wheel 32 will move further away from the wheel 30, thus increasing the tension in the track 16. Conversely, if the hydraulic ram is retracted, the opposite effect takes place and the tension in the track 16 diminishes.

Note that the tensioning system 44 can operate electrically or mechanically instead of hydraulically.

FIG. 2 illustrates in greater detail the mechanical relationship between the track 16 and the wheel 30. In this example of implementation, the wheel 30 works as a sprocket and engages drive lugs 57 on the track 16. Specifically, the track 16 has a carcass 52 having an outer face 54 and an inner face 56. Drive lugs 57 are mounted to the inner face 56. The drive lugs 57 are made from rubber material and are located at equally spaced intervals from one another. The drive lugs 57 fit in respective sockets 58 formed around the periphery of the sprocket 30. The dimensions of the sockets 58 and their spacing matches those of the drive lugs 57, such that as the sprocket 30 turns the drive lugs 57 mesh with the respective sockets 58.

The sprocket 30 that is shown in FIG. 2 includes a central disk-like structure 60 from which axially project a series of drive pins 62 defining between them the sockets 58. Accordingly, the sprocket 30 has two series of drive pins 62 one on each side of the disk-like structure 60. This arrangement allows using on the track 16 two series of drive lugs 57, each series meshing with a respective set of pins 62. FIG. 5 illustrates a front view of the sprocket 30, better showing the drive pins 62 which define the sockets 58. Note that in this arrangement the track is provided with drive lugs 57 arranged in two sets that extend parallel to one another along the internal surface of the track 16, leaving between them a space to receive the central disk-like structure 60 from which caries the drive pins 62. In particular, one set of the drive lugs 57 mesh with the drive pins 62 on one side of the central disk-like structure 60 (identified in the drawing by 61) while the other set of drive lugs 57 mesh with the drive pins 62 on the side 63 of the central disk-like structure 60.

The spacing between the sets of drive lugs 57 is selected such as to accommodate the width of the central disk-like structure 60. The central disk-like structure 60 has a smooth external surface and engages a corresponding smooth portion of the internal surface of the track 16. This allows the central disc-like structure to provide support for the track 16 and thus more evenly spread the loading on the internal surface of the track 16. Without such larger support surface, the track tension force will be distributed over the narrow area defined by the pins 62, which may be detrimental to the long term durability of the track 16.

While in practice the dimensions of the central disc-like structure 60 can vary depending on the specific application, it has been found that a disk like structure 60 having generally a width in the range of from about 40% to about 95% of the track width, preferably in the range of about 45% to about 95% and even more preferably from about 65% to about 95% of the track width, works well. For clarity, the width of the disk like structure is measured along the rotational axis of the sprocket 30, excluding the drive pins 62.

An alternative arrangement of the sprocket is shown in FIG. 3, which illustrates a front view of a sprocket 64, where the sockets 58 are formed in the center of the sprocket 64. In this arrangement the track 16 (not shown) has a single row of drive lugs 57, which are centrally located and mesh with the sockets 58. In this form of construction, the sprocket 64 includes a pair of discs 66, 68 that are spaced apart and connected to one another via the pins 62 which define between them the sockets 58. In this example, the discs 66, 68 are smooth surfaced and they engage corresponding smooth surfaced portions of the inner surface of the track, on either side of the row of drive lugs 57. As in the case with the previous embodiment, the discs 66, 68 contribute to support the track and prevent that the track tension is concentrated only on the drive pins 62. Again, in this instance the combined width of the discs 66, 68 is in the range of from about 40% to about 95% of the track width, preferably in the range of about 45% to about 95% and even more preferably from about 65% to about 95% of the track width.

The sprocket 30, 64 can transmit motion to the track 16 by two different mechanisms. The first is the friction drive mode and the second is the positive drive mode. During the friction drive mode, the friction developed between the peripheral surfaces of the discs 66, 68 and the flat inner surface of the track, which engages those surfaces is sufficient to drive the track. The tension which is built in the track 16 by operation of the tensioning system 44 can produce a significant amount of friction which is sufficient to drive the track 16. During the friction drive mode, the drive lugs 57 mesh with the sockets 58 but there is little pressure or strain acting on drive lugs 57.

Beyond a certain degree of power loading, the friction drive mode transitions to the positive drive mode. The reaction force operating on the track 16 as the vehicle 10 moves can overcome the friction between the track 16 and the peripheral surfaces of the discs 66, 68. This produces a small degree of slip between the peripheral surfaces of the discs 66, 68 until the drive lugs 57 firmly engage the pins 62. At that point no further slip is possible and the driving force is communicated to the track mostly via the drive lugs 57.

There are possible advantages to designing the sprocket such that it operates mostly in the positive drive mode, thus limiting the friction drive mode as much as possible. One such reason is proper engagement of the drive lugs 57 with the sockets 58. When the track 16 operates in the positive drive mode, the degree of tension in the track is high. The track 16 stretches to a small but measurable degree thus extending the spacing between the drive lugs 57, which effectively changes the pitch of the drive lugs. In addition, the drive lugs 57 which are in engagement with the sprocket 30, 64 also resiliently distort to some degree during engagement with the sockets 58, thus further altering the pitch. For that reason, the design of the sprocket 30, 64 in particular the spacing between the sockets 58 is a compromise design such that a proper engagement will occur with the drive lugs 57 and the sockets 58 both during the friction drive mode and the positive drive mode. Basically, the pitch of the sockets 58 is designed such that it can accommodate a slight variation in pitch of the drive lugs 57 on the track 16.

A more efficient sprocket design would be one where the pitch of the sprocket is designed to match a stable pitch of the track drive lugs 57.

In a specific and non-limiting example of implementation, the sprocket 30, 64 is designed to reduce as much as possible the friction drive mode. In a first embodiment, the surfaces 66, 68 engage the inside of the track in a rolling contact arrangement. FIG. 4 which illustrates this embodiment also illustrates an alternative track drive configuration which can be used as a conversion to retrofit a wheel based vehicle to tracked vehicle. The drive arrangement 70 includes a drive sprocket 72 and a pair of idler wheels 74 creating a triangular track pathway. An rubber track 76 is mounted on the sprocket 72 and the idler wheels 74. The track run 78 between the idler wheels 74 is the ground engaging run on which the vehicle is supported. The track 76 is otherwise similar to the track 16 in that it has drive lugs 57 used to positively engage the sprocket 72.

In this first embodiment the sprocket 72 uses centrally located sockets which engage respective drive lugs 57 of the track 76, similar to the arrangement illustrated at FIG. 3. That sprocket 72 provides on each side of the row of sockets two support surfaces 66 a, 68 a that engage the inside of the track 76. The support surfaces 66 a, 68 a engage the track 16 in a rolling contact. This is achieved by providing on the sprocket 72 a pair of axially spaced apart outer rings 80 that define at their outer periphery the support surfaces 66 a, 68 a and which engage the inside of the track 76. The outer rings are rotatably mounted on the sprocket core via rollers or any other suitable friction reduction arrangement. In this fashion, the outer rings 80 constitute the outer races of a bearing structure that rolls on the sprocket core.

The arrangement shown in FIG. 4 is designed such that the outer rings 80 can turn on the sprocket core freely in clockwise direction as well as in the counterclockwise direction. It may be desirable for some applications to allow the outer rings to turn freely (thus limit or negate the friction drive mode) only when the vehicle moves in one direction, say the forward direction. The friction drive mode would thus be maintained when the vehicle moves in the rearward direction. This unidirectional angular motion of the outer rings 80 can be achieved by providing the sprocket with a suitable agent (not shown in the drawings) that blocks the rotational motion of the outer rings 80 in a predetermined direction while permitting the movement in the opposite direction. This agent can be purely mechanical in nature, electrical, hydraulic, pneumatic or a combination thereof. An example of a mechanical agent is a ratcheting mechanism that uses spring biased teeth or pawls that retract when the outer rings 80 are turned in direction in which motion is permitted but fail to retract when rotation in an opposite direction is attempted, thus angularly locking the outer rings 80 to the sprocket core. Another possible implementation is to use locking friction pads, similar to a brake mechanism, that are retracted, thus allowing the outer rings 80 to rotate, but which can be extended, either electrically, mechanically, pneumatically or hydraulically to lock the outer rings 80 to the sprocket core. The locking friction pads are mounted to the sprocket core underneath the outer rings 80. When it is desired to allow the outer rings 80 to freely turn on the sprocket core, the locking friction pads are kept in their retracted position, out of contact with the outer rings 80. To block rotation the locking friction pads are extended radially until they engage the outer rings 80, preventing any further angular motion in any direction. This arrangement has the advantage of allowing more control freedom by selecting in real time the direction in which the outer rings 80 are allowed to turn or not turn in any direction. For such implementation, the arrangement is preferably under computer control using sensors to detect operational conditions and logic which establishes when to lock the outer rings 80. When the logic decides to lock the outer rings 80, it issues a control signal to the actuate the system driving the locking friction pads into engagement with the outer rings 80. This system is described in greater detail later, in relation to FIGS. 8 and 9.

Instead of using rollers 82 to allow the rotational movement of the outer rings 80 with relation to the sprocket core, the outer rings 80 can be mounted on the sprocket core such that the two components rotate one with relation to the other via a low friction interface, somewhat like a bushing arrangement. In this variant, the sprocket core has outer cylindrical surfaces on which are mounted the respective outer rings 80. A low friction material coating is provided on the outer cylindrical surfaces which provides a low friction contact interface such that the outer rings 80 can turn relatively freely on the sprocket core and maintain the rolling engagement with the track 76. Examples of low friction coatings that can be applied on one surface or both surfaces of the interfaces include polytetrafluoroethyle, urethane or any other suitable polymeric coating. A brass coating or insert is yet another possibility. In the event the low friction material can be used in conjunction with a lubricant, the material can be designed to carry a certain volume of the appropriate lubricant, such as oil or grease. For instance, the material can be made porous to hold a certain amount of lubricant.

With the above arrangement, the pins 62 are the only remaining component of the sprocket that engage the inner surface of the track 76 in a sliding contact (to the extent permitted by the play existing when the drive lugs 57 engage the pins 62). To reduce this sliding contact, the pins 62 can also be provided with rolling surfaces, as is illustrated at FIG. 6. In FIG. 6, the pins 62 are shown in cross-section and each pin carries a bushing 84 that is rotatably mounted on the pin 62 such as to create the desirable rolling contact with the portion of the track 76 that engages the pin 62/bushing 84. Instead of using a bushing 84, a bearing structure similar to the outer ring 80 shown in FIG. 4 can be used.

In a second possible embodiment, the friction drive mode is limited by providing the outer surface of the sprocket 72 with a treatment to reduce significantly the friction between the outer surface of the sprocket 72 and the inner surface of the track 16. In this embodiment, the sprocket 72 will include a core made of metallic material, coated with a different material that manifests a lower degree of friction with the inner surface of the track than the metallic material. In a specific example, the low friction treatment yields a coefficient of friction on the outer surfaces 66 a, 68 a of the sprocket 72 of less than about 0.1, preferably less than about 0.05 and even more preferably of less than about 0.01. The treatment may include the deposition on the outer surfaces 66 a, 68 a of the sprocket 72 a low friction material coating. In this example, the sprocket 72 engages with the inner surface of the track 76 via sliding contact (again to the extent permissible by the play allowed by the drive lugs 57 in the respective sockets). However, the sliding contact occurs at low power loadings and the system quickly transitions to the positive drive mode. Examples of low friction material can include polytetrafluoroethyle, brass plating and UHMW polyurethane, among others. It is possible to coat the entirety of the outer surfaces 66 a, 68 a of the sprocket 72 with the low friction material. Another option is to selectively coat the surfaces, such as coat only the surfaces 66 a and 68 a but not the pins 62. Yet another possibility is to apply a pattern of low friction material on the surfaces 66 a, 68 a, such as blocks of low friction material spaced apart from one anther and interspersed with areas that area uncoated and thus manifest a higher degree of friction with the inside surface of the track 76. Yet another possibility is to apply on the surfaces 66 a, 68 a of the sprocket 72 different types of low friction material. The coating pattern will depend on the desired degree of friction reduction between the sprocket 72 and the track 76.

In a possible variant, the sprocket arrangement illustrated in FIG. 4 is operated such as to selectively invoke or deactivate a friction drive assist that can be combined to the positive drive mode in order to potentially reduce the loading on the drive lugs 57.

This can be accomplished by providing the sprocket arrangement 72 with a device to lock the outer rings 80 to the sprocket core such that the outer rings 80 can no longer turn on the sprocket core. Examples of devices that can accomplish this function were discussed earlier. When the outer rings 80 are blocked against rotation in this fashion, the smooth surface of the track is no longer in rolling contact with the sprocket 72. Rather, the engagement is a frictional engagement which contributes to propel the track. Accordingly, the loading that propels the track is no longer concentrated on the drive lugs 57 alone since some of the driving force is channeled through the friction engagement.

The friction drive mode is essentially an assist that can be invoked during modes of operation in which the drive lugs 57 are subjected to high loading. Those modes of operation may arise when the vehicle climbs steep grades, pulls heavy loads or more generally requires a significant level of torque input in order to perform a certain task.

In order to determine the degree of loading on the drive lugs 57 it is possible to use a pressure sensor in the individual drive lugs 57. Each drive lug 57 or only some of the drive lugs 57 can be provided with pressure sensors to detect the pressure applied on the drive lugs 57 by the sprocket 30, 64, 72. The pressure sensor can be any type of pressure sensor suitable to provide a pressure reading when pressure is applied on one of the faces of the drive lug 57, the one that is engaged by a pin 62. Accordingly, as the pin 62 presses on the face of the drive lug 57, the pressure is sensed by the pressure sensor and an output signal is generated. FIG. 7 illustrates a possible example of implementation of a drive lug 57 in which is mounted a pressure sensor. To this end, the drive lug 57 can be designed with a suitable cavity 700 in which the pressure sensor 702 can be located. The pressure sensor 702 has a sensing part that is adjacent the face 704 of the drive lug 57 which is engaged by the pin 62. A battery can power the pressure sensor 702 and it is provided with a transmitter to wirelessly report pressure values to a receiver mounted on the undercarriage or at any other suitable location on the vehicle 10.

Advantageously, when multiple pressure sensors 702 are provided on the track 16, each pressure sensor 702 being mounted to a respective drive lug 57, each pressure sensor 702 is uniquely identified such that its pressure reading can be distinguished from pressure readings of other pressure sensors 702. Digitally encoding the pressure value reported by the pressure sensor 702 and appending to the pressure value a unique identifier can accomplish this. In this fashion, the receiver and the data processing unit that performs the analysis of the pressure values reported by the pressure sensors 702 can associate received pressure values to respective drive lugs 57.

In an alternative embodiment (not shown in the drawings), the pressure sensors 702 can be mounted to the sprocket 30, 64, 72, instead of being mounted to the drive lugs 57. In this fashion, the track 16 has no pressure sensing capability. The pressure sensors 702 are mounted on the sprocket 30, 64, 72 at locations that engage the drive lugs 57. In the examples of the sprockets described earlier, this would be the pins 62. The pins 62 are provided with cavities in which the pressure sensors 702 are mounted such that when the pins 62 engage the drive lugs 57, pressure registers on the pressure sensors 702.

A receiver (not shown) mounted on a suitable location on the vehicle 10 picks up the output of the pressure sensor 702. The signal is processed by a data processing device that will determine the loading on the drive lugs 57 and will then generate a control signal to selectively activate or deactivate the friction drive component.

Yet another possible way of implementing a pressure or loading sensor is to use a torque sensor in the power train that determines the amount of torque that is being applied on the sprocket 30, 64. Since the torque applied on the sprocket 30, 64 is directly related to the track 16 loading, then by reading the torque it is possible to deduce the amount of pressure acting on the drive lugs 57.

Yet another possibility is to use a drive lug loading sensor which indirectly determines the drive lug loading by observing the operational condition of the engine of the vehicle 10 and derives the amount of power, hence torque that is being produced. In this method of implementation the drive lug loading sensor uses a computer implemented engine parameters map that correlate engine parameters to torque produced by the engine. Possible engine parameters include RPM, throttle opening percentage, intake manifold pressure, amount of fuel being injected, temperature and ignition timing among others.

Accordingly the system can determine the torque generated at any given moment by searching the map on the basis of the current engine parameters to identify the corresponding torque value. Once the torque produced by the engine is known, the torque value applied on the sprocket 30, 64, 72 can be derived on the basis of the gear ratio that is being used to transmit the drive power from the engine to the sprocket 30, 64, 72.

FIG. 8 illustrates a block diagram of a non-limiting example of implementation of a data processing device 600. The data processing device 600 that is mounted on the vehicle is a computing platform having a CPU 602 that communicates with a machine-readable storage device 604 over a data bus 606. An input/output interface 608 connects to the data bus 606. Input signals that convey data to be processed by the data processing device 600 are received at the input/output interface 608. Similarly, output signals directed to components of the vehicle 10 which are controlled by the data processing device 600 also transit via the input/output interface 608.

The machine-readable storage medium 604 is encoded with software that is executed by the CPU 602. The software performs the processing of the inputs signals and generates output control signals on the basis of a control strategy.

The input signals that are applied to the input/output interface 608, include:

-   -   The output of the pressure sensor. As discussed previously, the         pressure sensor 702 reports the degree of loading acting on the         drive lugs 57. The signal stream, in addition to conveying         pressure information can also convey the identifier of the         respective pressure sensor 702 that has generated the data, when         multiple pressure sensors 702 are being used;     -   Output from operator console. This signal is generated in         response actuation of a control by the operator. The control may         be a mechanical control such as lever or button or may be an         electronic control. The control conveys a command to the data         processing device 600 to control the vehicle in a predetermined         fashion, by using as an input the pressure sensor 702. An         example of possible control includes enabling the engagement of         the friction drive component and the trigger point at which the         friction drive component will be engaged. The trigger point can         be the maximal degree of drive lug loading desired above which a         friction drive assist is to be used.     -   Torque information. In one example the torque information is         provided by a torque sensor indicating the torque acting on the         sprocket 30, 64, 72 and that is in turn acting on the track 16.         The degree of torque applied on the sprocket 30, 64, 72         determines to a large degree the degree of loading on the drive         lugs 57 and in that sense it can be an alternative to the         pressure sensor information. Note that instead of using a torque         sensor, the torque information can be derived by correlating the         engine parameters to the torque value, as discussed above.

The output signals that are released by the input/output interface 608 are as follows:

-   -   Sprocket lock-up. Controls the operation of a lock-up device to         prevent the outer ring 80 from rotating on the sprocket 30, 64,         72 in order to engage the friction drive assist mode.

The information that is received by the various inputs of the data processing module 600, in particular the input from the operator console, the pressure sensor 702 and the torque sensor is processed by software stored in the machine readable storage 604 in order to generate control signals that will manage the friction drive assist of the track 16. The logic built in the software determines the control strategy that will be implemented. One example of a control strategy is to engage the friction drive assist when the loading on the drive lugs 57 exceeds a certain threshold. A flowchart of the process that achieves this function is illustrated in FIG. 9. The process starts at 800 and determines at step 802 the degree of loading on the drive lugs 57. As discussed earlier, this can be done by reading the output of the pressure sensor(s) 702, the torque sensor or via the engine parameters. The result is then compared to a threshold at step 804. If the loading on the drive lugs 57 is too high the conditional step is answered in the affirmative and execution then proceeds to step 806 in which a control action is performed. The control action is to engage the sprocket lock-up device in order to lock the outer ring 80 to the sprocket 30, 64, 72 such that the outer ring 80 can no longer turn on the sprocket 30, 64, 72.

An example of such lock-up device is a set of locking friction pads, similar to brake pads that are mounted to the sprocket core and operate to engage the outer rings 80. Thus, when no friction assist is desired the locking friction pads are retracted and allow the outer rings 80 to freely rotate about the sprocket core. However, when the friction drive assist is desired the locking friction pads are actuated by extending them radially outwardly of the sprocket core such that they engage the inner surface of the outer rings 80, thus preventing the outer ring 80 from rotating about the sprocket core. In this fashion, the outer rings 80 are locked with relation to the sprocket core and provide a friction drive assist.

Those skilled in the art will appreciate that when the track 16 is worn out, a track replacement operation needs to be performed. If effectuated using a prior method, this operation can be complicated and time consuming since it requires the removal and subsequent re-installation of the idler wheels 74 and possibly other components of the track support system in which the drive lugs 57 of the track are engaged.

With a view to alleviating this difficulty, FIGS. 10 and 11 illustrate in greater detail the structure of a sprocket 64 a in accordance with a specific non-limiting embodiment of the present invention, in which removal of a worn out track is facilitated. The sprocket 64 a is a variant of the sprocket 64, and is provided with a central hub 70 a that mounts to the axle of the vehicle via bolts 72 a. A series of radially extending spokes 74 a project from the hub 70 a. The spacing between the spokes 74 a is selected such as to match the pitch of the drive lugs 57 since the spokes 74 a define between them sockets 58 a which receive the drive lugs 57. On the outer periphery of the spokes 74 a are mounted a pair of spaced apart discs 66 b, 68 b (also referred to as side rings).

In this example of implementation, the structure of the sprocket 64 a is such that the sockets 58 a receiving the drive lugs 57 can be opened to allow the drive lugs 57 to exit and enter the respective sockets along a direction of movement that is generally parallel to the rotation axis of the socket 58 a. When the sockets 58 a are so opened, the track 16 can be removed by simply pulling it out of the socket 58 a (sliding the track along the rotational axis of the socket 58 a) and there is no need to completely dismount the socket 58 a from the vehicle.

FIG. 12 illustrates the sprocket 64 a of FIG. 10 but in which the sockets 58 a have been laterally opened thus allowing removal of the track 16. The lateral opening of the sockets 58 a is achieved in this example by the removal of the side rings 66 b, 68 b as it will be discussed later. Note that the removal of both side rings 66 b, 68 b is not necessary in practice since the sockets 58 a need to be opened only on one side (the external side of the vehicle) in order to allow the removal of the track 16. FIG. 13 illustrates this particular arrangement where only the side ring 66 b has been removed, the side ring 68 b being still mounted on the sprocket 64 a and being shown in dotted lines.

Note however, there may be applications in which it may be desirable to allow both side rings 66 a, 68 a to be removed such as to provide a completely symmetrical sprocket. In this fashion the sprocket 64 a can be installed in one of two possible orientations without any impact on its functionality in terms of allowing the removal of the track 16. This is useful in instances where some wear may occur and flipping the sprocket 64 a over allows evening out of the sprocket wear.

FIG. 16 is a top view of the sprocket 64 a shown in FIG. 13, illustrating the sockets 58 a laterally opened on the left side with the side ring 68 b remaining in place.

The mounting system which allows the selective removal of the side rings 66 b, 68 b is illustrated in greater detail in FIGS. 14 to 19. The mounting system uses fasteners coupling the side rings 66 b, 68 b to the spokes 74 a. When the fasteners are removed, the outer rings 66 a, 68 a laterally slide out of the sprocket 64 a, thus laterally opening the sockets 58 a. Each side ring 66 b, 68 b is made of metallic material and it is dimensioned to have an internal diameter that is slightly larger than the external diameter of the spokes 74 a. In this fashion, as best shown in FIGS. 15 and 17 the outer rings 66 b, 68 b sit on top of the spokes 74 a. Fasteners 76 a connect the side ring 66 b, 68 b to each spoke 74 a. The fasteners 76 a include a bolt 78 a engaging a nut 80 a which sits in a countersunk hole made on the outer surface of the side ring 66 b, 68 a. In this fashion, the nuts 80 a are flush with the outer surface of the side rings 66 b, 68 b and do not protrude therefrom. The number of bolts used to retain the side rings 66 b, 68 b to each spoke 74 a can vary. In the illustrations, a single fastener 76 a is being shown per spoke 74 a, however more than one can be used if desired. Alternatively, some spokes 74 a may not receive any fastener.

In order to remove the side rings 66 b, 68 b the fasteners are loosened with the appropriate tool. The bolts 78 a are removed completely by sliding them out of their holes. This is possible since the removal operation takes place on the side of the sprocket 64 a that is laterally exposed and easily accessible. Generally the location of the fasteners that hold the side rings 66 b, 68 b is within the area that is defined by the circular periphery of the sprocket 64 a; this area is laterally accessible to allow removal of the fasteners as access to this area is not impeded by the track 16.

After the bolts 78 a are removed, the nuts 80 a remain in their respective countersunk holes and are removed with the side ring 66 b, 68 b. When each bolt 78 a has been removed, the side ring 66 b, 68 b simply slides out of the sprocket 64 a along the direction shown by the arrow 82 a. Note that before this operation can be effected, it would be preferable to release the tension in the track 16 by bleeding down the hydraulic pressure in the tensioning system 44. Since there may still be some degree of residual tension in the track 16, a pry bar or any other suitable tool can be used to forcibly pull out the side ring 66 b, 68 b against the friction generated by the internal surface of the track 16.

FIG. 18 illustrates an alternative arrangement where the side rings 66 b,68 b have a peripheral flange 70 a that abuts on the lateral edges of the spokes 74 a. Bolts 84 a secure the flange to the spokes 74 a. In this instance, the bolts 84 a are also easily removable while the track 16 is still engaged on the sprocket 64 a since access to the bolts 84 a with a tool is possible from the lateral side of the sprocket 64 a. After all the bolts 84 a have been removed the side ring 66 b, 68 b is removed thus allowing the track 16 to slide out of the sprocket 64 a.

FIG. 19 is yet another possible variant of the sprocket 64 a where the side ring 66 b, 68 b has a flange 86 a that is positioned internally and which is used to fasten the side ring 66 b, 68 b to the spokes 74 a. Note in this instance, the spokes 74 a are narrower and have lateral faces 88 a to allow the flanges 86 a to abut with them in a face-to-face relationship. To provide sufficient radial support to the side rings 66 b, 68 b the rings are provided with stiffening webs 90 a. The stiffening webs extend radially with respect to the side-rings 66 b, 68 b and they abut the lateral faces 88 a. Additional fasteners are provided at 92 a to secure the webs 90 a to the spokes 74 a.

In a yet another possible variant, the rings 66 b and 68 b can be integrally formed with drive pins 74 b such that these three components can be removed or installed on the sprocket core as a single unit. This arrangement is illustrated at FIGS. 17 a and 17 b. The outer rings 66 a, 66 b and the drive pins 74 b thus form an integral outer ring 79 sitting atop the spokes 74 a. The arrangement is such that the drive pins 74 b register with the respective spokes 74 a but in a variant this registration may only be partial (only some of the drive pins 74 b register with spokes 74 a) or simply nonexistent (none of the drive pins 74 b register with the spokes 74 a). The advantage of this arrangement is to allow complete removal of the component of the sprocket that is in contact with the track. Thus in addition to facilitating the removal and installation of the track on the vehicle, the outer ring 79 can be easily replaced when some of its components are worn out. For instance, if the drive pins 74 b wear out as a result of vehicle operations in conditions in which abrasive material gets lodged between the track and the sprocket, such as sand or gravel, it makes it possible to quickly replace the outer ring 79 with a new unit having drive pins 74 b with nominal dimensions.

The outer ring 79 is attached to the sprocket core as per the method described in connection with FIG. 17, using bolts 78 a that fasten the outer ring 79 to the respective spokes 74 a.

In accordance with another specific non-limiting embodiment, now described with reference to FIG. 20, there is provided a sprocket 64 b, which is a variant of the sprocket 64. The sprocket 64 b may be made as a casting. This is done for cost reasons. However, the casting operation imposes a certain number of design constraints on the sprocket. One of those constraints is the geometric shape of the drive pins or bars 62 b that require a so called “draft angle” in order to be able to carry out the moulding operation. The draft angle is best shown at FIG. 20. Instead of being straight and of a constant cross-sectional shape, the drive pin or bar 62 b is narrowed at the center in order to create an angle alpha (α) which is of sufficient magnitude to allow the removal of the sand. Typically, this angle α is in the range of about 1 degree to about 25 degrees. A drive pin or bar 62 b with such a cross-sectional shape creates a particular stress pattern on the drive lugs 57 that are normally made with flat faces. As a result, the drive pin or bar 62 b concentrates the pressure on the drive lug face near the side edges of the drive lug 57 with is detrimental to drive lug and can accelerate the drive lug 57 wear. To overcome this problem embodiments of the present invention provide an improved drive lug 70 b that has a cross-sectional shape which follows to at least some extent the shape of the drive pin or bar 62 b in order to allow a more even pressure distribution over the face of the drive lug 70 b. FIG. 20 shows the drive lug 70 b with relation to the drive pin or bar 62 b. For clarity, the sprocket 64 b in use turns along the direction A and therefore the drive pin or bar 62 b engages the face 72 b of the drive lug 70 b to drive the track 16 b. The drive lug 70 b has a cross-sectional profile such that the thickness of the drive lug 70 b (the thickness is the dimension of the drive lug 70 b measured along the direction of rotation A or the direction along which the track 16 b is driven) manifests an enlargement located at a point intermediate the lateral extremities 76 b, 78 b of the drive lug 70 b. In a specific example of implementation the enlargement is at midpoint between the lateral extremities 76 b, 78 b.

The enlargement is a straight line rib that runs from a major portion of the distance between the tip of the drive lug 70 b and the base of the drive lug. In a specific example of implementation, the rib runs for the entire distance from the tip to the base. The drive face of the lug 70 b defines a pair of flat surfaces that meet at an angle defining the rib between them.

The profile of the drive lug 70 b is made to match the profile of the drive pin or bar 62 b such that when the drive pin or bar 62 b engages the drive lug face 72 b the pressure distribution over the drive lug face 72 b will be more even, by comparison to the prior art arrangement where the pressure is concentrated near the lateral edges 72 b, 78 b. The degree to which the enlargement projects from the imaginary plane 80 b depends to a large extent on the draft angle α; the larger the angle the larger the enlargement will extend. Also note that if the profile of the drive pin or bar 62 b is different from what is shown in the drawings, for instance the profile is such that the narrowed area 82 b is not in the center of the drive pin or bar 62 b, rather it is offset to one side or to the other side, the lateral location of the enlargement could also be shifted such that it matches the location of the area 82 b. In this fashion, the drive pin or bar 62 b has a shape that is complementary to the drive lug drive face 72 b in order to achieve a more uniform pressure distribution over the drive lug 70 b.

Note that the face 84 b of the drive lug 70 b which is opposite the face 72 b is also provided with an enlarged portion 86 b such that it is symmetrical to the face 84 b. In this fashion, when the track is run in reverse, in which case the face 86 b is the face which receives the driving force from the sprocket 64 b, the pressure loading on the face 86 b is also more evenly distributed.

In some cases, the pin or bar 62 b may have a curved shape, in which case the drive lug face 72 b can be imparted a matching curved shape to achieve more balanced pressure distribution.

In other cases, the drive lug face 72 b may be flat, despite the pins 62 b being non-flat (e.g., narrowed at the center). Under these circumstances, relatively even pressure distribution between a lug 70 b and a pin 62 b can be achieved by providing a sleeve 101 that fits over the pin 62 b. This embodiment is shown in FIGS. 20 a and 20 b. The sleeve 101 may have an exterior surface that is of generally constant cross-sectional dimension along its length such that, when the sleeve is fitted over the drive pin 62 b, the exterior surface will engage the lug face 72 b along its entire length and thus evenly distribute the pressure over the lug face 72 b.

The sleeve 101 has an outer generally cylindrical shape. Note that other shapes are also possible without departing from the spirit of the invention. Internally, the sleeve defines a cavity 103 which is complementary to the shape of the drive pin or bar 62 b. In this fashion, the drive pin or bar 62 b can snugly fit inside the cavity 103. The cavity 103 thus has the reverse shape of the drive pin or bar 62 b. In the example shown in the drawings, the cavity 103 has at its center a narrowed section 105 corresponding to the midpoint constriction of the drive pin or bar 62 b. On both sides of the narrowed section 105 are formed enlargements 107 and 109. In this fashion, the wall thickness of the sleeve 101, which is the thickness of the wall between the internal cavity 103 and the outer lug contacting surface varies along the length of the sleeve 101. The wall is thickest at a location that is between the extremities of the sleeve 101, and preferably but not necessarily is at mid-point of the sleeve. The wall thickness progressively diminishes from the thickest point toward each sleeve 101 extremity.

The sleeve 101 may be made of synthetic material such a polyurethane or any other suitable plastic material that has adequate durability characteristics. Alternatively, the sleeve 101 can be made of metallic material. The sleeve 101 can be formed on the drive pin or bar 62 b by overmolding. This operation involves placing the drive pin or bar 62 b in a mold and injecting in the mold the material forming the sleeve 101. In this fashion the material takes the shape of the drive pin or bar 62 b and solidifies around it. This would produce a continuous sleeve 101 around the drive pin or bar 62 b. This embodiment is shown in FIG. 20 b. Note that for practical reasons, such overmolding operation would be performed simultaneously over each drive pin or bar 62 b of the sprocket. The mold is thus designed to receive the sprocket in its entirety and has internal partitions that define cylindrical void volumes around each drive pin or bar 62 b.

Alternatively, the sleeve 101 can be manufactured as a multi-component device that is mechanically mounted or adhesively connected to the drive pin or bar 62 b. More specifically, the sleeve 101 can be cast or otherwise manufactured as two halves that mate and encase the drive pin or bar 62 b. Fasteners such as screws can be used to attach the two halves together.

In accordance with yet another specific non-limiting embodiment of the present invention, FIG. 21 illustrates the structure of a sprocket 64 c, which is yet another variant of the sprocket 64. FIG. 22 shows a similar view but of a prior art design. The prior art design is identified by the reference numeral 70 c. The sprocket 70 c is a multi component device which includes a hub 72 c that contains drive gears which are part of the power transmission system. In particular, the hub 72 c includes a planetary gearing system that includes one or more outer (or planetary) gears which revolve around the axis of rotation of the sprocket 70 c, and also include one or more internal sun gears that mesh with the planetary gear. In use, power is supplied to the sun gear(s) which in turn drive the planetary gear resulting into rotational motion being imparted to the sprocket 70 c. The hub 72 c has an outer housing 74 c on which is provided a flange 76 c. The outer sprocket structure 78 c that engages the track is bolted to the flange 76 c. The outer sprocket structure 78 c or rim is provided with an internal inwardly projecting flange 80 c that abuts in a face to face relationship with the flange 76 c. Both flanges 76 c and 80 c are secured to one another via suitable fasteners, such as bolt inserted through registering bolt holes 82 c. This prior art design is objectionable because it is bulky; the flange to flange attachment is such that the outer sprocket structure 78 c projects outwardly (along the direction A) by a distance that is at least equal to the thickness of the flange 76 c. This implies that for installations where it is desirable to recess the outer sprocket structure 78 c as much as possible, the options are limited because of the requirement to provide a mounting flange 76 c to which the outer sprocket structure 78 c is to attach.

The example of implementation of the invention shown in FIG. 21 overcomes this problem by forming the sprocket rim 84 c integrally with the hub 86 c. In this instance, the hub 86 c has a casing 88 c to which is mounted the planetary gear and that meshes with the one or more sun gears. Since there is no longer a requirement for a mounting flange, the outer sprocket structure 84 c can now be mounted closer to the imaginary reference plane B by comparison to the prior art arrangement shown in FIG. 22. In addition, the connection between the rim 84 c can be made sturdier by using more material which makes the entire sprocket more resistant and also reduces flexion between the hub 86 c and the rim 84 c.

FIG. 35 is a cross sectional view that illustrates the internal construction of the sprocket 64 c. The hub 86 c which is integrally formed with the rim 84 c defines an internal cavity 87 in which is mounted the planetary gear system. The planetary gear system includes a ring gear that is integrally formed with the casing 86 c. A sun gear 91 which is connected to the drive axle of the vehicle drives the ring gear 89 via a set of gears 93.

In a different example of implementation illustrated in FIG. 23, the drive pin 62 c of the sprocket 64 c is provided with a wear jacket 90 c which is designed to protect the pin 62 c against wear. The wear jacket 90 c is a two piece device, including first piece 92 c and a second piece 94 c that meet along a parting plane 96 c to fully enclose the pin 62 c. When the first and second pieces 92 c, 94 c are mated to one another, they form between them a cavity that is complementary to the shape of the pin 62 c. In this fashion both first and second pieces 92 c, 94 c can be mounted to the pin 62 c and form around the pin 62 c a protective jacket which prevents the rubber material of the track 16 c to be in contact directly with the pin 62 c. While the wear jacket 90 c is susceptible to wear out over time, it is intended to be a replaceable item.

The first and second pieces 92 c, 94 c connect with one anther by bolts 98 c.

A possible variant is shown in FIG. 24. The wear jacket 100 c includes a first half 102 c and a second half 104 c that are connected to one another via mechanical arrangement 106 c which can be a clip or may also use fasteners. The resulting wear jacket 100 c is free to rotate around the pin 62 c and thus forms a bushing which allows reducing the frictional contact between the sprocket 64 c and the track 16 c.

After the wear jacket 100 c is worn out, it is replaced by removing the used wear jacket 100 c and installing a new one. The installation is done by placing each half 102 c, 104 c of the wear jacket on the pin 62 c and attaching the halves 102 c, 104 c to the pin 62 c.

The wear jacket can be made of a suitable synthetic material providing a low friction surface or may also be made of a metallic material.

Note that for the embodiments shown in FIGS. 23 and 24 the wear jacket does not need to slip on the pin 62 c, which would require access to one of the extremities of the pin 62 c. Rather, the halves of the wear jacket are mated to one another along a direction that is generally transverse to the pin 62 c axis. This makes the installation easier.

FIG. 25 is yet another possible variant which uses drive pins whose radial position can be adjusted to compensate for wear (which has a tendency to reduce the diameter of the sprocket). The sprocket arrangement has a series of radially adjustable drive pins 108 c. The extremities of the drive pins 108 c are mounted in respective grooves 110 c in end plates 112 c which extend transversally to the rotation axis of the sprocket. In this fashion, the drive pins 108 c are free to move radially in their respective grooves in the direction shown by C.

A suitable locking system is provided in order to move the drive pins in the desired position and lock the drive pins in that position. Various types of the locking systems can be used. One example, shown in FIG. 26 is a rod 114 c which threadedly engages the drive pin 108 c and which can be rotated by any suitable means, such as an electric motor, in order to displace the drive pin 108 c radially in the groove 110 c. The movement of the drive pins 108 c can be synchronized such that all the pins 108 c move in unison. This can be accomplished in many different ways, one being the provision of a mechanical drive system that rotates all the rods 114 c at the same time and by the same degree.

FIG. 28 shows yet another possible refinement in which the sprocket 116 c is provided with resilient drive pins 118 c. The drive pins 118 c have a component 120 c that is mounted via a resilient element 122 c to another component 124 c which can be part of the drive pin 62 c or can rest against another part of the sprocket. In this fashion the floating component 120 c can resiliently yield when it is engaged by a drive lug 57 of the track 16 c.

The resilient element 122 c can be a spring or a block of resilient material such as rubber.

FIG. 27 is yet another possible variant in which the pitch of the sprocket can be varied. In this arrangement the extremities of the drive pins 118 c are mounted in a peripheral channel 124 c formed on end plates 126 c (a single end plate is shown in the drawings). In this fashion, the drive pins 118 c are circumferentially movable independently from one another thus allowing varying the spacing between them, hence the pitch of the sprocket. The means for moving the drive pins 118 c may include actuators 124 c that may be hydraulic, pneumatic or electric. In a specific example of implementation, the actuators 124 c are synchronized such that the change of pitch of the sprocket is uniform. The synchronization is done via a control system that triggers the extension or the retraction of the actuators by a controlled amount in order to achieve the desired degree of displacement, hence pitch change.

In yet another specific non-limiting embodiment, now described with reference to FIG. 29, the track 16 has an outer ground engaging surface 16 b and an opposite inner surface 16 a. the track 16 is supported by a series of wheels that define a generally triangular track motion path. That path has a lower run 18 which is a ground engaging run. When the vehicle is being driven it is supported on the ground engaging run 18.

In this specific non-limiting embodiment, the series of wheels that support the track 16 include a drive wheel 30 a which is mounted on top, two generally opposite idler wheels 32 a and a series of mid-rollers 24 mounted between the idler wheels 32 a. The mid-rollers 24 engage the inner surface of the ground engaging run to maintain the ground engaging run 18 in contact with the ground during the operation of the vehicle. The mid-rollers 24 are mounted on a suspension system (not shown) allowing the mid-rollers 24 to yield upwardly when the vehicle rides over obstacles.

FIGS. 30 and 31 illustrate in greater detail the mechanical relationship between the track 16 and the drive wheel 30 a. In this example of implementation, the drive wheel 30 a works as a sprocket and engages drive lugs 26 projecting from the inner surface 16 a of the track 16. The drive lugs 26 are made from rubber material and are located at equally spaced intervals from one another. The drive lugs 26 fit into respective sockets 28 formed around the periphery of the sprocket 30 a. The dimensions of the sockets 28 and their spacing matches those of the drive lugs 26, such that as the sprocket 30 a turns the drive lugs 26 mesh with the respective sockets 28.

In this example of implementation, the drive lugs 26 are centrally located on the track 16. In a possible variant, the drive lugs could be offset laterally, toward one side edge of the track 16.

The drive lugs 26 and the corresponding set of sockets 28 constitute a first positive drive connection between the sprocket 30 a and the track 16. The undercarriage 10 includes an additional drive connection that is also gear-like, including projections on the track 16 that mesh with complementary recesses on the sprocket 30 a. This additional drive connection spreads around the loading applied on the track to drive it, which otherwise would be concentrated at any given moment on the few drive lugs 26 engaging the sprocket 30 a.

The additional drive connection is spread over a larger surface area of both the sprocket peripheral surface and the track inner surface 16 a. More specifically, the additional drive connection includes a series of teeth 120 which engage complementary recesses 122 on the sprocket 30 a.

The teeth 120 are smaller in height than the drive lugs 26. In a specific and non-limiting example of implementation, a ratio between the height of a drive lug 26 and a tooth 120 is in the range from about 0.05 to about 0.25, preferably in the range of about 0.12 to about 0.2 and most preferably of about 0.1 to about 0.166.

In a specific example, the teeth 120 are a multiple of the main drive lug 26. For instance there could be 6 teeth 120 per main drive lug 26 or less.

Also, the pitch of the two positive drive systems are different. The ratio between the pitch of the drive lugs 26 and the pitch of the teeth 120 is in the range from about 0.05 to about 0.25, preferably in the range of about 0.12 to about 0.2 and most preferably of about 0.1 to about 0.166.

A ratio between the length (the length is the dimension measured along a direction that is transverse to the track 16) of a drive lug 26 and a tooth 120 is in the range from about 0.05 to about 0.25, preferably in the range of about 0.12 to about 0.2 and most preferably of about 0.1 to about 0.166.

As illustrated in the drawings, in particular in FIG. 31, the length of the teeth 120 extends the full width of the track 16. This is not an absolute requirement as the teeth 120 can have a length that is less than the width of the track 16. In a specific example, the ratio between the length of a tooth 120 and the width of the track 16 is in the range from about 0.1 to about 1 (broad range), preferably in the range of about 0.5 to about 1 (intermediate range) and most preferably of about 0.75 to about 1 (narrow range).

Since the teeth 120 are relatively small in terms of height, the idler wheels 32 a do not need to be provided with complementary recesses to accommodate the teeth 120. Accordingly, the circumferential surfaces of the idler wheels 32 a that engage the teeth 120 can be smooth surfaced. Alternatively, those surfaces can be made with complementary recesses as in the case of the sprocket 30 a.

In a specific and non-limiting example of implementation, the ratio between the diameter of an idler wheel 32 a and the height of the teeth 120 is in the range from about 0.018 to about 0.01, preferably in the range of about 0.0166 to about 0.0133 and most preferably of about 0.0153 to about 0.0143.

A ratio between the diameter of the idler wheel 32 a and the pitch of the teeth 120 is in the range from about 0.045 to about 0.025, preferably in the range of about 0.0415 to about 0.033 and most preferably of about 0.0383 to about 0.03575.

As shown in FIG. 32, the mid-rollers 24 are shorter than the full width of the track 16 and engage only a portion of the inner surface 16 a of the track 16. The width of the mid-rollers 24 is such that they abut the drive lugs 26 which constitute an alignment mechanism to keep the track 16 along the correct path of travel over the ground engaging run 18. Alternatively, the mid-rollers 24 can be made to extend the full length of the track 16; however they would require a central clearance to accommodate the drive lugs 26. Yet another possibility is to provide an additional mid-roller set 24 a, that is internal and that also engages the drive lugs 26 on their sides such as to more positively maintain the alignment of the track 16.

The mid-rollers 24, 24 a can be smooth surfaced or can be provided with recesses matching the teeth 120.

In a specific and non-limiting example of implementation, the ratio between the diameter of a mid-roller 24 and the height of the teeth 120 is in the range from about 0.0308 to about 0.02, preferably in the range of about 0.029 to about 0.0234 and most preferably of about 0.029 to about 0.025.

A ratio between the diameter of the mid-roller 24 and the pitch of the teeth 120 is in the range from about 0.077 to about 0.05, preferably in the range of about 0.0725 to about 0.0585 and most preferably of about 0.0725 to about 0.0625.

In a possible variant, the undercarriage can be modified to use only the teeth 120 for driving the track 16. In other words, the drive lugs 26 and the corresponding sockets 28 on the sprocket 30 a would be omitted.

In another possible variant, the pattern of the teeth 120 can be changed and does not always need to be such that the teeth 120 extend perpendicular to the longitudinal axis of the track 16. For example:

-   -   The teeth 120 can angled, as shown in FIG. 33. In this fashion         the teeth 120 would engage the corresponding teeth on the         sprocket 30 a gradually causing them to run more smoothly.     -   The teeth 120 can be arranged in chevrons, as shown in FIG. 34         which has the advantage of cancelling any lateral thrust that         angular teeth 120 would create on the track 16.

In any of the aforementioned alternative teeth patterns, corresponding patterns would also be required on the sprocket 30 a, and possibly also on the idler wheels 32 a.

Although various embodiments have been illustrated, this was for the purpose of describing, but not limiting, the invention. Various modifications will become apparent to those skilled in the art and are within the scope of this invention, which is defined more particularly by the attached claims. 

1-6. (canceled)
 7. An endless track for traction of a vehicle, the endless track comprising: an outer ground engaging surface; an inner surface opposite the outer ground engaging surface; and a plurality of drive lugs projecting from the inner surface, one or more of the plurality of drive lugs having opposite lateral extremities and a driving face extending between the lateral extremities for engagement by a sprocket in order to propel the track, the driving face having a projection intermediate the lateral extremities that contacts the sprocket when the drive lug engages the sprocket.
 8. An endless track as defined in claim 7, wherein the drive lug has a tip portion and a base portion adjacent the inner surface, the projection extending over a major portion of the distance between the base portion and the tip portion.
 9. An endless track as defined in claim 8, wherein the driving face includes a first flat surface and a second flat surface, the first flat surface and the second flat surface meeting at an angle along a common boundary which defines the projection.
 10. In combination: a) a drive sprocket having a generally circular configuration with a generally cylindrical peripheral surface, the drive sprocket comprising a plurality of spaced apart drive pins or bars defining recessed sockets on the cylindrical peripheral surface; and b) an endless track having an outer ground engaging surface, an inner surface opposite the outer ground engaging surface and a plurality of drive lugs projecting from the inner surface for engagement in respective ones of the sockets, one or more of the plurality of drive lugs having opposite lateral extremities and a driving face for engagement by a respective drive pin or bar, the drive pin or bar having a recessed portion and the driving face having a projection that engages the recessed portion when the drive pin or bar engages the driving face. 11-23. (canceled)
 24. An endless track for traction of a vehicle, the endless track comprising: a ground-engaging outer surface; an inner surface opposite to the ground-engaging outer surface; and a plurality of drive lugs projecting from the inner surface to engage a drive wheel to impart motion to the endless track, the drive wheel comprising a plurality of drive members distributed around the drive wheel, each drive lug of the plurality of drive lugs comprising a driving surface for contacting a drive member of the plurality of drive members when the drive lug engages the drive member, a dimension of the drive lug in a longitudinal direction of the endless track varying in a widthwise direction of the endless track such that: the drive lug comprises a given one of a projecting portion and a recessed portion and the drive member comprises the other one of the projecting portion and the recessed portion; and the projecting portion is received in the recessed portion when the drive lug contacts the drive member.
 25. The endless track claimed in claim 24, wherein the given one of the projecting portion and the recessed portion is the projecting portion.
 26. The endless track claimed in claim 25, wherein an apex of the projecting portion of the drive lug is located in a central region of the drive lug in the widthwise direction of the endless track.
 27. The endless track claimed in claim 26, wherein the apex of the projecting portion of the drive lug is located substantially at a midpoint of the drive lug in the widthwise direction of the endless track.
 28. The endless track claimed in claim 25, wherein the drive lug comprises a tip and a base that is adjacent the inner surface and the projecting portion of the drive lug extends over at least a majority of a distance between the tip and the base of the drive lug.
 29. The endless track claimed in claim 25, wherein the driving surface of the drive lug comprises a first flat area and a second flat area that are oriented differently to define the projecting portion of the drive lug.
 30. The endless track claimed in claim 25, wherein the driving surface of the drive lug comprises an angular part defining the projecting portion of the drive lug.
 31. The endless track claimed in claim 30, wherein the angular part of the driving surface of the drive lug defines an oblique angle.
 32. The endless track claimed in claim 25, wherein the driving surface of the drive lug comprises a curved part defining the projecting portion of the drive lug.
 33. The endless track claimed in claim 25, wherein the recessed portion of the drive member defines an angle.
 34. The endless track claimed in claim 33, wherein the angle defined by the recessed portion of the drive member is between about 1° and about 25°.
 35. The endless track claimed in claim 33, wherein the angle defined by the recessed portion of the drive member is a draft angle used in manufacturing the drive wheel.
 36. The endless track claimed in claim 25, wherein the projecting portion of the drive lug comprises a rib running in a height direction of the drive lug.
 37. The endless track claimed in claim 24, wherein: the projecting portion is a first projecting portion; the recessed portion is a first recessed portion; the driving surface of the drive lug is a first driving surface; the drive lug comprises a second driving surface opposite to the first driving surface to contact the drive member when the drive lug engages the drive member as the endless track is moved in a reverse direction opposite to that in which the first driving surface contacts the drive member; the drive lug comprises a given one of a second projecting portion and a second recessed portion and the drive member comprises the other one of the second projecting portion and the second recessed portion; and the second projecting portion is received in the second recessed portion when the drive lug contacts the drive member as the endless track is moved in the reverse direction.
 38. The endless track claimed in claim 37, wherein: the given one of the first projecting portion and the first recessed portion is the first projecting portion; and the given one of the second projecting portion and the second recessed portion is the second projecting portion.
 39. A track system for traction of a vehicle, the track system comprising: a drive wheel comprising a plurality of drive members distributed around the drive wheel; and an endless track to be driven by the drive wheel, the endless track comprising: a ground-engaging outer surface; an inner surface opposite to the ground-engaging outer surface; and a plurality of drive lugs projecting from the inner surface to engage the drive wheel to impart motion to the endless track, each drive lug of the plurality of drive lugs comprising a driving surface for contacting a drive member of the plurality of drive members when the drive lug engages the drive member, a dimension of the drive lug in a longitudinal direction of the endless track varying in a widthwise direction of the endless track such that: the drive lug comprises a given one of a projecting portion and a recessed portion and the drive member comprises the other one of the projecting portion and the recessed portion; and the projecting portion is received in the recessed portion when the drive lug contacts the drive member. 